As the IoT takes hold and wearable technology advances, the smartphone will still be there to provide the raw computing power and connectivity to co-ordinate and communicate with all these new devices. The idea of adding sensors to a phone, either integrated or tethered via Bluetooth is a powerful concept. In some parts of the world, an air quality sensor would be popular, as is the idea of a carbon monoxide sensor for home safety.
We can see this already taking place in many areas of research. For example, last year researchers at the University of California, Los Angeles (UCLA) developed a device that can turn any smartphone into a DNA-scanning fluorescent microscope. The implications for medical diagnostics are profound and show once again how the smartphone can be leveraged to bring down the costs of healthcare as well as bring cutting edge diagnostics to the developing world.
To conclude, the smartphone revolution is just warming up. The market will continue to be driven through use cases and the development of innovative sensors rather than through radical changes to the smartphone itself.